Inkage contact operating mechanism for electric circuit breaker

ABSTRACT

A pivotally mounted contact arm and releasable latch lever, retained by a current-responsive latch system, are interconnected by a toggle linkage, the knee of which is connected by tension springs to a manually movable handle operable to collapse and straighten the toggle to effect opening and closing movement, respectively, of the contact arm. A cam follower is pivotally suspended from the connection joining the toggle linkage and latch lever and has a free end interposed between a fixed cam and one link of the toggle, the follower being drawn along the cam by movement of the latch lever when released to break the knee overcenter of the linkage, accelerate the collapse of the toggle, and restrain the upper toggle link to prevent contact-arm rebound.

United States Patent 2,357,210 8/1944 Leonard Donald A. Link l-lubertus, Wash.;

Fred H. Williams, Milwaukee, Wis. 67,146

Nov. 16, 1971 Cutler-Hammer, Inc.

Milwaukee, Wis.

Inventors Appl. No. Patented Assignee TOGGLE LINKAGE CONTACT OPERATING MECHANISM FOR ELECTRIC CIRCUIT BREAKER 6 Claims, 5 Drawing Figs.

Primary ExaminerRalph F. Staubly Attorneys-Hugh R. Rather and William A. Autio ABSTRACT: A pivotally mounted contact arm and releasable latch lever, retained by a current-responsive latch system, are interconnected by a toggle linkage, the knee of which is connected by tension springs to a manually movable handle operable to collapse and straighten the toggle to effect opening and closing movement, respectively. of the contact arm. A cam follower is pivotally suspended from the connection joinin g the toggle linkage and latch lever and has a free end interposed between a fixed cam and one link of the toggle, the follower being drawn along the cam by movement of the latch lever when released to break the knee overcenter of the linkage, accelerate the collapse of the toggle, and restrain the upper toggle link to prevent contactarm rebound.

PATENTEnuqv 161921 3, 21 ,1e9

SHEET 1 OF 2 Douala ff. Lin/2' 7nd if. Wiffiams "If/V .ftmrrnay PATENTEDunv 1s l97| SHEET 2 [IF 2 I nventm: Donal ol ffiz'nk 7nd if. Wiffiams WVK Attorney TOGGLE LINKAGE CONTACT OPERATING MECHANISM FOR ELECTRIC CIRCUIT BREAKER BACKGROUND OF THE INVENTION This invention relates to molded case electric circuit breakers and more particularly to an improvement in a collapsible toggle linkage for opening the contacts of the breaker.

In circuit breakers of the above type, it is a known expedient to locate the movable contact at the free end of a pivotally mounted contact arm which is driven open and closed by the collapsing and straightening of a toggle linkage connected thereto. The toggle may be manually collapsed and straightened by movement of a handle connected to the knee of the toggle through tension springs which supply the normal quick opening and closing drive force for the contact arm.

The other end of the toggle linkage is connected to a latch lever normally retained in a fixed position by a currentresponsive latch system. When released due to an excessive current condition, the latch lever moves under the influence of the tension springs to carry the respective end of the toggle linkage in a direction wherein the inclusive angle between the links of the toggle is reduced to initiate collapse of the toggle. The movement in reverse directions of the knee and one end of the toggle under the influence of the heavy tension springs provides a generally rapid collapse of the toggle and separation of the contacts. However, under large overcurrent conditions, a still quicker separation is needed to reduce the amount and severity of arcing. To accomplish this stronger springs are commonly employed and in certain prior art types, fixed surfaces are provided to interact with the toggle to cam the knee in its toggle-collapsing direction. The camming action can be made to accelerate the movement of the link and reduce rebound of the contact arm and it is to such a feature that this invention is directed.

SUMMARY OF THE INVENTION It is therefor a primary object of this invention to provide an improved operating mechanism for an electric circuit breaker.

It is a specific object of this invention to provide a collapsing-toggle-operating mechanism for an electric circuit breaker having an improved camming arrangement for accelerating the collapse of the toggle mechanism in response to an overcurrent condition.

It is a further specific object of this invention to provide a collapsing-toggle-operating mechanism for an electric circuit breaker having an improved arrangement for preventing rebound of the movable contact arm.

These and other objects and advantages of the invention will become more apparent in the following specification and claims when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a molded case circuit breaker shown partially in elevation but with a portion broken away to expose the operating mechanism and contact structure of this invention shown in the contact closed position.

FIG. 2 is a fragmentary view in cross section of the operating mechanism and contact structure of FIG. 1 but shown in a manually operated contact opened position;

FIG. 3 is a fragmentary view in cross section of the operating mechanism and contact structure similar to FIG. 2 but shown in an automatically operated contact opened position;

FIG. 4 is a fragmentary view of the operating mechanism taken generally along the line 4-4 in FIG. 1; and

FIG. 5 is an enlarged fragmentary view of a portion of the operating mechanism as shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT The circuit breaker illustrated in the drawings is generally referred to as being of molded case construction wherein the breaker mechanism is housed within a molded insulating case 2 and cover 4 secured together by conventional means such as screws, rivets or the like (not shown). The circuit breaker may be a single or multipole device, the individual poles each having a line terminal and contact plate assembly 6, a stationary contact 8, a movable contact 10, a pivotally supported contact arm 12 and a load terminal and plate assembly 14. Each pole is further provided with a current-sensing means 16 of the thermal or magnetic type or a dual-sensing system employing both types, operable upon an overload current condition to move a common trip bar 18 extending across all the poles.

Each contact arm 12 is carried between the sides of individual frames 20 which in turn are separately secured to a common insulated shaft assembly 22 which extends across all poles of the breaker. The shaft assembly 22 is rotatably supported in a pair of spaced mounting brackets 24 secured upon the floor of molded case 2. A compression spring 25 is disposed between the frame 20 and contact arm 12 in the area of the contact 10 to provide contact pressure for the breaker.

The operating mechanism for the circuit breaker is located in one pole of the breaker to drive that particular movable contact assembly and the common shaft 22 which drives the contact assemblies of the remaining poles. In the breaker shown in the drawings, the operating mechanism includes a latch lever 26 mounted on a pivot pin 28 secured between the mounting brackets 24 near their upper ends. A pair of parallel upper toggle links 30 are pivotally attached to the latch lever by a pivot pin 32 to depend from the latch lever. A pair of parallel lower toggle links 34 are pivotally attached to the op posite sides of the frame 20 of the pole containing the operating mechanism by a pivot pin 36 to extend upwardly from the frame toward the depending ends of links 30. A knee pin 38 provides a common pivotal connection for the adjacent ends of the upper and lower toggle links 30 and 34, respectively.

The operating means further includes an operating lever 40 which overlies the linkage and mounting brackets 24 and has depending side legs which are pivotally supported on the external sides of mounting brackets 24. A pair of helical tension springs 42 are connected between the knee pin 38 and the upper portion of operating lever 40 which spans the side legs. A molded insulating handle 44 is cooperatively shaped to rest upon the operating lever 40 and be maintained in position thereon by engagement with the inner portion of cover 4. Handle 44 projects externally of the enclosing case through an elongated opening 46 in cover 4 to pennit manual movement of the operating lever 40.

The circuit breaker is further provided with a double-acting latch system operable to restrain the otherwise free end of latch lever 26. The latch system includes a primary latch 48 pivotally mounted between the brackets 24 on a pin 50 fixed to the brackets at its ends. Latch 48 has an upstanding leg 52 thereon which is provided with an opening for receiving the end of latch lever 26 and a depending leg 54 having a stepped lower edge to provide a latching surface between the stepped levels. A torsion spring 56 is disposed around pin 50 to engage latch 48 and one bracket 24 at its ends, thereby providing a counterclockwise bias for the latch.

A secondary latch member 58 is also pivotally mounted between the mounting brackets 24 on a pin 60 fixed to the brackets. Secondary latch 58 has a horizontally projecting L- shaped leg 62 which engages with the stepped surface on lower leg 54 of latch 48 to restrain the latter against the combined actions of the counterclockwise bias of torsion spring 56 and the urging of the latch lever 26. Secondary latch 58 also is provided with a torsion spring 64 disposed around pin 60 and is connected between the latch 58 and one of the mounting brackets 24 to bias the secondary latch 58 counterclockwise, thereby urging leg 62 against the stepped edge of lower leg 54 on latch 48. A leg 66 is also formed on secondary latch 58 to project upwardly at substantially right angles with the leg 62 thereon. Common trip bar 18 is secured to the leg 66 at its upper end, the trip bar 18 extending transversely of the breaker housing whereby the current-sensing means 16 of each pole of the breaker may engage the bar 18 to actuate the latching system.

The circuit breaker is shown in the contact closed position in FIG. 1. Latch 48 of the latching system restrains latch lever 26 in a fixed position to thereby fixedly locate the uppermost pivot pin 32 of the toggle linkage. Handle 44 is moved to the right-hand end of opening 46 in cover 4 to pivot the operating lever 40 in a clockwise direction. The latter movement carries the upper ends of springs 42 overcenter of the pivot pin 32 which then act upon the knee pin 38 to cause it to move to the right and straighten the linkage. Movement of the knee pin to the right is limited by engagement of the upper toggle links 30 with portions 68 of the mounting brackets 24. The straightening action of the linkage drives the lower pivot pin 36 downward to pivot frame 20 and common shaft 22 in a clockwise direction thereby causing downward motion of the contact arms 12 of all the poles to effect closing of the movable contacts upon the stationary contacts 8.

Opening of the contacts is accomplished manually by moving handle 44 to the left-hand end of opening 46 to return the line of action of springs 42 overcenter of the pivot pin 32 to the original position as shown in FIG. 2. The springs 42 act upon knee pin 38 to move it to the left, thereby causing the linkage to collapse which raises the lower pivot pin 36 and pivots the frame 20, shaft 22 and contact arm 12 counterclockwise to separate the contacts 8 and 10. The counterclockwise movement of frame is limited by engagement thereof with the portions 68 of mounting brackets 24.

Opening of the contacts automatically in response to an overcurrent condition is accomplished by means of the latching system in cooperation with the current-sensing means and is shown in FIG. 3. Excessive current in the closed circuit path of any pole of the breaker is sensed by the overcurrentsensing means 16 of that particular pole. Sensing means 16 moves against common trip bar 18 in response to an overcurrent condition to pivot the secondary latch 58 clockwise, thereby releasing the primary latch 48 which in turn is moved counterclockwise by virtue of the combined actions of spring 56 and the urging of latch lever 26 to cause the release of the latter. When released, the latch lever 26 moves in a clockwise direction about pivot pin 28 due to the influence of springs 42 and in so doing carries the upper pivot pin 32 of the toggle linkage overcenter of the line of action of the springs 42 to collapse the linkage and open the contacts.

Automatic operation of the circuit breaker signifies that the contacts must interrupt a greater magnitude of current than under normal operating conditions. Interruption of increased magnitudes of current causes more severe arcing conditions and damage within the breaker. To improve the circuit interrupting capabilities of circuit breakers during automatic trip operation, means are provided to more rapidly separate the contacts and therefore more rapidly extinguish the arc drawn therebetween.

The circuit breaker disclosed herein is provided with a camming structure to accelerate the collapse of the toggle linkage, thereby causing more rapid contact separation. The camming structure primarily consists of a cam surface 70 on the portion 68 of one of the brackets 24 and a cooperating cam follower 72 pivotally mounted on pivot pin 32 to depend along the upper link 30. Cam follower 72 has a cylindrical projection 74 on one side surface, the periphery of which is disposed between and in engagement with one of the upper toggle links and the cam surface 70. The follower 72 also has a tab 76 formed over to the side surface opposite that of the projection 74 to be received within an oblong opening 78 in latch lever 26 to permit the follower 72 limited movement relative to the latch lever 26 but to prevent the follower from falling away from the cam surface 70 in the manual OFF position.

It can be seen in FIG. I that in the ON" or closed contact position, the projection 74 on cam follower 72 rests within a shallow recessed portion of the cam surface 70. An overcurrent condition in the breaker operates the latch system to 75 release latch lever 26. Springs 42, acting through knee pin 38, upper links 30 and pivot pin 32, urge the latch lever in a clockwise direction about pivot pin 28. The projection 74 on cam follower 72 engages the forward edge of upper link 30 to serve as a pivot point or fulcrum for the link 30. Movement of the upper end of the link 30 and pivot pin 32 in a clockwise direction to the right in the drawings will cause the lower end of link 30 and the knee pin 38 to move to the left in a togglecollapsing direction. The point of engagement of projection 74 with the edge of upper link 30 is particularly close to the pivot pin 32 to provide a high ratio of movement for the knee pin 38 with respect to movement of pivot pin 32. Continued clockwise movement of the latter about pin 28 draws the cam follower 72 therewith which causes the projection 74 to move upward along the relatively vertical portion of the cam surface 70. The latter movement of the projection 74 along surface maintains the fulcrum point provided by projection 74 on the edge of link 30 at a substantially constant distance from the pivot pin 32 but at a changing distance from the pivot pin 28 to increase the ratio of reverse movement between pivot pin 32 and knee pin 38 further accelerating knee pin 38 and to afford a prying action upon the link 30 to move the knee pin end thereof to the left with respect to the drawings.

The accelerated movement of knee pin 38 to the left causes a faster collapse of the toggle linkage which thereby quickly separates the contacts 8 and 10 a distance sufficient to prevent the restriking of an arc therebetween and thereby shortens the duration of the arc. The movable pans of the system engage fixed stops in a conventional and well-known manner to limit the opening movement. However, due to the mass of the movable contact arms 12 and the rapid movement imparted thereto, a strong rebound force has to be overcome to prevent the contacts from reclosing to a distance wherein an arc can be redrawn. The prying action of projection 74 upon upper link 30 by virtue of the favorable ratio between pins 32 and 38 under the heavy force of tension springs 42 overcomes such rebound tendencies of the contact arms 12.

We claim:

1. An electric circuit breaker comprising, in combination:

an insulating case;

a stationary contact in said case;

movable contact means pivotally mounted in said case;

operating means including mounting brackets therefor secured within said case and further comprising:

a latch lever releasably restrained between said mounting brackets.

an operating lever pivotally supported on said mounting brackets and having handle means projecting externally of said case;

a collapsible toggle linkage having a first link pivotally connected at one end thereof to said latch lever, a second link pivotally connected at one end thereof to said movable contact means, and a knee pin commonly joining the opposite ends of said first and second links of said toggle, said knee pin being connected to said operating lever by tension spring means to effect alternate straightening and collapsing of said toggle linkage in response to manual movement of said operating lever between extreme positions thereof;

current responsive latch means operable to release said latch lever to also effect collapse of said toggle linkage;

a cam surface on said mounting brackets;

a cam follower pivotally mounted for movement with said latch lever and having a portion thereof disposed between and in engagement with said cam surface and said first link to serve as a fulcrum for said first link when said latch lever is released, said released latch lever moving said first link about said portion in one direction to move said knee pin in an opposite, toggle-collapsing direction.

2. The combination according to claim 1 wherein said cam follower is pivotally supported from the pivotal connection joining said first link and said latch lever and depends therefrom along said first link.

3. The combination according to claim 2 wherein said portion on said cam follower engages the edge of said first link at a point near the pivotal connection of said first link and said latch lever to afford a mechanical advantage to said first link wherein movement of said knee pin in said opposite direction is amplified with respect to movement of the other end of said first link.

4. The combination according to claim 3 wherein movement of said latch lever draws said portion along said cam surface to effect an increasing ratio of movement between said knee pin and the pivotal connection joining said first link to said latch lever to accelerate movement of said knee pin in the 6 toggle-collapsing direction.

5. The combination according to claim 4 wherein movement of said cam follower along said cam surface acts upon the edge of said first link to exert a prying action upon said toggle linkage in the direction of movement of said portion along said cam surface.

6. The combination according to claim 2 wherein said cam follower is provided with a tab portion formed over and loosely received within an opening in said latch lever to limit the movement of said cam follower relative to said latch lever. 

1. An electric circuit breaker comprising, in combination: an insulating case; a stationarY contact in said case; movable contact means pivotally mounted in said case; operating means including mounting brackets therefor secured within said case and further comprising: a latch lever releasably restrained between said mounting brackets. an operating lever pivotally supported on said mounting brackets and having handle means projecting externally of said case; a collapsible toggle linkage having a first link pivotally connected at one end thereof to said latch lever, a second link pivotally connected at one end thereof to said movable contact means, and a knee pin commonly joining the opposite ends of said first and second links of said toggle, said knee pin being connected to said operating lever by tension spring means to effect alternate straightening and collapsing of said toggle linkage in response to manual movement of said operating lever between extreme positions thereof; current responsive latch means operable to release said latch lever to also effect collapse of said toggle linkage; a cam surface on said mounting brackets; a cam follower pivotally mounted for movement with said latch lever and having a portion thereof disposed between and in engagement with said cam surface and said first link to serve as a fulcrum for said first link when said latch lever is released, said released latch lever moving said first link about said portion in one direction to move said knee pin in an opposite, toggle-collapsing direction.
 2. The combination according to claim 1 wherein said cam follower is pivotally supported from the pivotal connection joining said first link and said latch lever and depends therefrom along said first link.
 3. The combination according to claim 2 wherein said portion on said cam follower engages the edge of said first link at a point near the pivotal connection of said first link and said latch lever to afford a mechanical advantage to said first link wherein movement of said knee pin in said opposite direction is amplified with respect to movement of the other end of said first link.
 4. The combination according to claim 3 wherein movement of said latch lever draws said portion along said cam surface to effect an increasing ratio of movement between said knee pin and the pivotal connection joining said first link to said latch lever to accelerate movement of said knee pin in the toggle-collapsing direction.
 5. The combination according to claim 4 wherein movement of said cam follower along said cam surface acts upon the edge of said first link to exert a prying action upon said toggle linkage in the direction of movement of said portion along said cam surface.
 6. The combination according to claim 2 wherein said cam follower is provided with a tab portion formed over and loosely received within an opening in said latch lever to limit the movement of said cam follower relative to said latch lever. 